[alt-photo] Re: Chemical Development for Printing Out Processes

[Ryuji Suzuki]

In order for the developer to discriminate exposed AgX crystals from unexposed 
ones, the crystals in the emulsion must be exceptionally "clean" meaning free of 
defects that act as fog center. It goes without saying that the crystals must 
not be exposed to any light that can create latent image center, as well. These 
are very important factors when making silver gelatin emulsions for developing 
process. Printing out process emulsions are full of crystalline defects and when 
electrons are injected through the developer they are going to develop with 
ease, with or without intense exposure required to produce print out images. The 
result is dense fog.

Old physical developers can act in somewhat different way, by adjusting the 
reduction potential of the developer to a level that's barely enough to reduce 
silver ion from the solution on bulk metallic silver surface (c.f. silver 
intensifier). That's why I suggested to experiment with developer exhausted by 
actual developed out print processing, that is, lower developer concentration, 
lower pH, and some reducible silver complex ion in the solution. Even then, it 
will be a somewhat tricky task because the window of reduction potential that 
does not cause massive fog but still augment the image development will be 
fairly narrow.

--
Ryuji Suzuki
"No matter how much you study or improve vacuum tubes, you will not arrive at a
transistor." (Leo Esaki)


Richard Knoppow wrote:
>
> ----- Original Message ----- From: "Francesco Fragomeni" <fdfragomeni at gmail.com>
> To: "The alternative photographic processes mailing list"
> <alt-photo-process-list at lists.altphotolist.org>
> Sent: Friday, September 07, 2012 9:12 PM
> Subject: [alt-photo] Re: Chemical Development for Printing Out Processes
>
>
>> Ryuji,
>>
>> Thanks for the reply. So your thought is that the higher ph and potency of
>> a modern developer (unused) would cause fog in a POP emulsion. Interesting
>> and I hadn't considered that but it makes sense as a possibility.
>>
>> By the way, I'm not particularly interested in recreating the results of
>> historic literature or figuring out what works best for the purpose, hence
>> the question about using modern developers with POP emulsions. Its a
>> mismatch intentionally. My interest is simply in seeing what the results
>> might be simply for the sake of curiosity.
>>
>> Has anyone actually tried this who can confirm Ryuji's fog hypothesis? Or,
>> do any of you Albumen practitioners have an extra test strip and some
>> Amidol or other print developer sitting around that you can test with next
>> time you print? I'm still setting up my space otherwise I'd try it.
>>
>> Thanks for contributing Ryuji and anyone else who chimes in.
>>
>> -Francesco
>>
> Perhaps Ryuji can explain the differences in developing out and printing out
> coatings. I have only a little understanding of this but I believe POP coatings
> do not allow the developer to discriminate between exposed and unexposed silver
> crystals, at least not very much.
> The usual process for POP whether gelatin-silver or salt or albumin is to allow
> light generated silver to form and then intensify it using a suitable toner. The
> unused silver halide is removed either co-incident with the toning or afterward.
> Some toners are not suitable because they will tone all the silver regardless of
> whether it in metallic form or not. Here again, I am not sure I understand why a
> gold toner, for instance, will tone an unfixed POP print while something like a
> sulfiding toner will simply turn the whole thing to silver sulfide. Fixing
> before toning tends to remove the image silver along with the non-metalic
> silver, perhaps because it is so fine.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
>
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